As described elsewhere, with narrowband + wideband images, one can extract an estimate of the narrowband emission line devoid of the background signal inevitable infesting the narrowband image. Each image in this set of images begins with the extraction of the estimated emission-line components and the subsequent combination of those line components into an RGB image in some way. Unlike my previous ventures into isolating emission-line components, this time, I treated the OIII line as two lines: a line contributing to the blue broadband image and one contributing to the green broadband image. This approach enables supplementing the respective broadband images' intensities in proportion to the OIII contribution that each receives. For instance, in a HOO image formed this way, the OIII in the green channel could differ in intensity than the OIII in the blue channel. Furthermore, if present, the difference represents reality better than an arbitrary assignment of some arbitrary or estimated percentage of the OIII signal (contaminated with background) to the green and blue channels.

IMAGE A: This image uses RGB supplemented by the 3xHa and 2xOIII. The background-free emission-line components of Ha, OIII-green, and OIIIb (OIII-blue) were extracted. Then 3x the Ha emission line supplemented to the red broadband image, 2x the OIIIg (OIII-green) emission line supplemented the green broadband image, and 2x the OIII-blue emission line supplemented to the blue broadband image.

IMAGE B: This is a narrowband image HOO, with two differences. Firstly, the H and O are the emission-line estimates, background free, rather than the H and O as acquired. Secondly, this image uses the separate estimates of the OIIIb and OIIIg.

Of course, both of these renditions suffer from an overprint of my style of image processing. By the way, all the processing on the nebula took place on starless images, with the RGB stars reintroduced afterward. These images have been downsampled about 2::1

Data: RGBSHO from an image-processing contest data set (https://www.astrobin.com/forum/c/off-topic/anything-goes/processing-competition-to-win-time-on-the-chile-cdk-17/). CDK17, Chile.